Hindukid, charging more for a phone call at 2 PM than 10 PM is just as reasonable as charging more for a 5 PM flight than a 10 PM flight. Supply and demand in action. Price discrimination is when two people pay different fares to fly on the same 5 PM flight, or the same 10 PM flight.

Even WN doesn't sell all the seats on their planes for $200 coast-to-coast, yet they have enough $200 seats for sale to cause the other airlines to match the fare. WN doesn't require a Saturday night stay, nor do they charge outrageous walk-up fares, yet they consistently make a higher profit than other airlines. WN doesn't print money, so it must be possible. The reason is labor costs and un-productivity are out of control at the other majors.

I don't know anything about the Indian domestic air market, so I can't comment on the reason for high fares there.